1. Field of the Invention
The present invention relates, generally, to contour measuring devices, and particularly to a contour measuring device with an error correcting unit for automatically and accurately compensate for errors in measurements.
2. Discussion of the Related Art
In the manufacturing of precision objects such as optical components (lenses) and other industrial components (ball bearings) the need exist to determine whether manufacturing errors are within acceptable tolerance. Such manufacturing errors may include the differences between the design dimensions and the manufactured dimensions of the object. Measured dimensions of the manufactured object are usually regarded as the actual dimensions. Precision measuring devices are used to measure the manufactured objects, and the more precise the measuring device, the better. Precision measuring devices, are of two types: contact-type precision measuring device and contactless-type precision measuring device. The contact-type precision measuring device has a probe that touches and traces the contour of the object. The contactless-type precision measuring has an optical probe for emitting light towards the objects.
As indicated above, both contact-type contour measuring device and contactless-type contour measuring device are commonly used to measure the contours of precision objects. Referring to FIG. 13, a typical contour measuring device 30 includes a horizontal platform 31, a pair of guide rails 32 fixed on the horizontal platform 31, and a movable fixture 33 disposed on the guide rails 32. The movable fixture 33 includes a probe 331. The probe 331 can be a touch trigger probe or an optical probe. If the probe 331 is a touch trigger probe, the probe 331 will touch an object 34 during contour measurement of the object 34. If the probe 331 is an optical probe, the probe 331 will emit light towards the object 34 and the light reflected off the object 34 could be captured and processed in order to obtain the contour measurement of the object 34.
Inherently, the contour measuring device 30 exhibits errors such as linear errors (linear errors along an X-Y plane, and an X-Z plane) of the guide rails 32, and motion errors (rotation errors along an X-axis direction, a Y-axis direction, and a Z-axis direction) of the movable fixture 33. Therefore, the measured contour value of the object 34 is subjected to errors during the measuring process, thereby decreasing the accuracy of the measured contour values. However, the linear errors of the guide rails 32 can be determined in advance, and the measured contour value can be compensated according to the linear errors previously determined. However, the linear errors determined in advance are generally different in each measuring processes, thus the measured contour value may not be compensated accurately in each measuring process.
Therefore, a contour measuring device which can automatically and more accurately compensate measured contour value is desired.